Al-Si-Sn Bearing alloy and bearing composite

ABSTRACT

An aluminum base bearing alloy having outstanding seizure resistance, particularly under high loads, and having good fatigue resistance and wear resistance is provided. The alloy comprises, in addition to aluminum, 5-11 wt. % Si and 1.5-35 wt. % Sn and contains at least 5 nodular Si particles having a diameter of at least 5 μm per 3.56×10 -2  (mm) 2  of cross-sectional area of the alloy. The bearing alloy may optionally contain at least one additional element selected from Pb, In, Tl, Cd, Bi, Cu, Mg, Cr and Mn. A bearing material is provided by pressure welding the aluminum base bearing alloy to a backing steel sheet.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to aluminum base bearing alloys and bearing materials and, particularly, to aluminum base bearing alloys in which a specified number of silicon particles of a specified size are dispersed in the aluminum matrix.

(2) Background of the Invention

Aluminum alloys are widely used as bearings in internal combustion engines, e.g., as connecting rod bearings and crankshaft bearings in automobile and marine engines. These bearings are resistant to corrosion in the engine environment and thus are highly advantageous for such use.

Materials employed as bearings in internal combustion engines are required to withstand high loads and high temperatures. Much effort has been directed in recent years, therefore, to providing aluminum base bearing alloys having high resistance to seizure, fatigue and wear under the conditions encountered in these engines.

U.S. Pat. No. 4,153,756 discloses Al-Sn base bearing alloys having a low degree of softening and, consequently, high fatigue strength, under high temperature conditions. The alloy is provided by adding chromium or zirconium to a basic alloy consisting of 10 to 30 wt.% tin and the remainder aluminum. Copper or both copper and beryllium can also be added to the alloy.

Al-Sn base bearing alloys comprising 3.5-35 wt.% of Sn, 0.1-1.0 wt.% of Cr and 1-10 wt.% in total of one or more members selected from Si, Cr, Mn, Sb, Ti, Zr, Ni and Fe, the remainder being aluminum, are also disclosed in the prior art as having high fatigue strength and, additionally, good wear resistance.

G. C. Pratt and C. A. Perkins in a paper entitled "Aluminum Based Crankshaft Bearings for the High Speed Diesel Engine", SAE Technical Paper Series 810199 (1981), describe the development of an engine bearing lining alloy for the high speed diesel engine and which has the composition Si (11 wt.%), Cu (1 wt.%) and the remainder Al. The alloy is described as having superior seizure resistance as compared to lead bronze on test rigs under conditions of sparse lubrication and controlled misalignment. It is further described that the casting procedure adopted and the subsequent processing of the alloy to bimetal ensure that the silicon particles are restricted to a few microns in size and that the silicon particle size is an important factor in determining the extent of compatibility (defined in the paper as the resistance of a bearing alloy to local welding on to a steel counterface); the highest degree being obtained only when there is a complete absence of coarse particles. The casting procedure and processing of the alloy to bimetal, however, are not described.

The mere inclusion of silicon in an aluminum base bearing alloy, however, does not ensure that the bearing alloy will possess consistently superior resistance to seizure, fatigue and wear under the severe loads and temperature conditions encountered in modern internal combustion engines and, particularly, in automobile engines which have shafts made of spheroidal, or nodular, graphite cast iron or other coarse material.

It is an object of the present invention, therefore, to provide an aluminum base bearing alloy and bearing composite which consistently possesses a superior balance of seizure, fatigue and wear resistance under high loads and high temperatures and when used as a bearing surface with nodular cast iron materials.

SUMMARY OF THE INVENTION

According to the present invention this and other objects are obtained by providing an aluminum base bearing alloy which contains 5-11 wt.% Si and 1.5-35 wt.% Sn and in which at least 5 particles of Si which have a nodular, or "lumpy", shape and a diameter of at least 5 μm are provided per 3.56×10⁻² (mm)² of cross-sectional area of the bearing alloy. The bearing alloy of the invention may optionally include up to 8 wt.% of Pb, In, Tl, Cd or Bi; up to 2 wt% of Cu or Mg and up to 1 wt.% of Cr or Mn for providing other desired properties.

In another embodiment of the invention a bearing material is provided by pressure welding the bearing alloy to a backing steel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing seizure unit loads (seizure resistance) of aluminum base bearing alloys according to the present invention as a function of Si content of the alloy.

FIG. 2 is a graph showing seizure unit loads versus silicon content of alloys having the same composition as those of FIG. 1 but in which the Si particle size and shape are not controlled.

FIG. 3 is a graph showing a comparison of wear resistance versus Si content of aluminum base bearing alloys according to the present invention with that of similar alloys in which Si particle size is not controlled.

FIG. 4 is a graph showing fatigue unit loads (fatigue resistance) of aluminum base bearing alloys according to the present invention as a function of the Si content of the alloys.

FIG. 5 is a graph showing seizure unit loads of an aluminum base bearing alloy according to the present invention and of a conventional Al-Sn-Cu alloy as a function of oil temperature.

FIG. 6 is a graph comparing seizure unit loads of an aluminum base bearing alloy according to the present invention with those of a conventional Al-Sn-Cu alloy as a function of the type of supported shaft.

DESCRIPTION OF PREFERRED EMBODIMENTS

The aluminum base bearing alloy according to the present invention contains 5-11 wt.% of Si and 1.5-35 wt.% of Sn. Amounts of Si of less than about 5 wt.% Si do not provide the outstanding seizure resistance of alloys of the present invention under conditions of high load and/or the use of low viscosity oil (although the fatigue resistance of such alloys are higher and can be used under conditions which demand a high fatigue limit). Amounts of Si of more than about 11 wt.% are not desirable and reduce the strength of the alloy.

The silicon (Si) is present in the form of precipitates in the aluminum matrix of the alloy of the invention. At least 5 particles per 3.56×10⁻² (mm)² of cross-sectional area of the bearing alloy of the Si must be in the form of nodular particles having a diameter of at least 5 μm. As employed herein to define the shape of the particles, the term "nodular" is intended to mean an irregular, rounded lump as opposed to flat flake-like or needle-like particles. Nodular particles are required since flat or needle-like particles are brittle and may tend to disintegrate during use and adversely affect the antiseizing properties of the bearing alloy.

Also, as employed herein, the term "diameter" is intended to refer to the maximum dimension of a particle when viewed in a particular cross-sectional area of the alloy as explained below.

At least 5 nodular Si particles having a diameter, or size, of 5 μm must be provided in a cross-sectional area of the bearing alloy of 3.56×10⁻² (mm)². The area of 3.56×10⁻² (mm)² is chosen for convenience and is based on the viewing area of the microphotography equipment of the inventors. The number of Si particles per unit area can be modified by employing the appropriate conversion factors. For example, the above-described particle number/area limitation corresponds to 1.4×10⁸ particles per m². It is also noted that the number of particles per cross-sectional area of the bearing alloy is that determined in a horizontal cross-section of a sheet of the alloy, i.e., a cross-section that is parallel to the surface of the sheet (and viewed in a direction perpendicular to the surface thereof) when prepared according to a process as described below. The size of Si particles measured in a vertical cross-section of a sheet of the alloy is smaller than that measured in a horizontal cross-section. Additionally, it is noted that the quantity limitations described above may not be fulfilled on the surface of a sheet of the alloy directly after its machining.

If the nodular particles of silicon are less than 5 μm, the bearing alloy will not have exceptional seizure or wear resistance. On the other hand, there is a practical upper limit of about 40 μm for the size of the Si particles because with bearing alloys containing particles above about 40 μm machining of the bearings becomes difficult.

To achieve the desired levels of seizure resistance the number of the nodular particles above 5 μm per 3.56×10⁻² (mm)² of cross-sectional area of the alloy must be at least 5. The maximum number of particles of any given size is of course limited by the amount of Si contained in the alloy. Typically, the desired properties of the aluminum base bearing alloys of the present invention are achieved when the number of Si particles having a size of at least 5 μm and, particularly, having a size between 5-40 μm is less than the maximum number of particles possible based on the amount of Si contained in the alloy; the balance of the Si being particles of less than 5 μm.

Seizure resistance of the bearing alloy according to the present invention increases as the size of the nodular Si particles increases. On the other hand, the number of larger particles is limited because the larger particles tend to decrease the fatigue resistance of the bearing alloys. To obtain bearing alloys having the highest seizure resistance, the bearing alloy of the invention will preferably contain, per 3.56×10⁻² (mm)² per cross-section area, at least 5 particles having a diameter of 5 to 10 μm and at least 5 particles greater than 10 μm in diameter. More preferably, the alloy will contain, per said unit area, at least 5 particles having a size of 5 to 10 μm, at least 5 particles having a size greater than 10 μm and at least 1 particle greater than about 17 μm (and less than about 40 μm for the reasons noted above). However, for bearing alloys according to the present invention having the highest level of seizure resistance, the fatigue resistance is somewhat lower as may be seen by referring to the data of the tables presented below.

The outstanding seizure resistance of the bearing alloy according to the present invention in which the shape, size and number of Si particles are controlled according to the limitations described above is believed to be due to the ability of the Si particles to prevent the well-known adhesion phenomenon between aluminum base bearings and the shafts supported thereby and to reduce the surface roughness of the shafts. Aluminum tends to rub off onto a rotating shaft and to adhere thereto and there is a tendency for the aluminum on the shaft to adhere to that of the bearing. It is believed that the nodular Si particles tend to remove the aluminum from the shaft.

The apparent ability of the silicon particles of the aluminum base bearing according to the present invention to reduce the surface roughness of the shaft to be supported by the bearing is most pronounced with the use of shafts having a hard and coarse surface and, particularly, with the use of nodular graphite cast iron shafts. With conventional aluminum base bearings, grinding burrs which are formed around the graphite particles on the surface of the shaft tend to grind, or wear, the surface of the bearing material. The nodular Si particles of the alloy according to the present invention, however, are believed to smooth over the roughness of the surface of the nodular shafts because of the number and size of the hard Si particles. It is noted that the improved wear resistance and antiseizing property of the bearing alloy according to the present invention is not obtained unless the shape, size and number of the Si particles are controlled as noted above.

The seizure resistance, fatigue resistance and wear resistance of the bearing alloy according to the present invention are determined according to tests under dynamic loads which are described more fully below in conjunction with specific embodiments of the alloy. These properties cannot be defined easily in quantitative terms because the values depend on the design of the testing equipment and test conditions and such equipment and conditions are not standard in the art.

The aluminum base bearing alloy according to the present invention also contains tin in an amount of 1.5-35 wt.%. The tin is added mainly for the purpose of lubrication. An amount of tin of greater than 35%, although improving conformability and low friction properties, reduces the hardness and strength of the bearing alloy. On the other hand, if the amount of tin is less than 1.5%, the bearing alloy is too hard and does not have sufficient conformability. The addition quantity of the tin within the range of 1.5-35 wt.% can be determined according to the expected use of the bearing alloy. Generally, the amount of tin is low if the bearing is to be employed under large loads. For use under light loads, the amount of tin can be higher. The seizure resistance of the bearing alloy of the present invention is also increased as the amount of tin is increased.

In other embodiments of the aluminum base bearing alloy according to the present invention, the alloy, in addition to containing the silicon and tin, may also contain at least one element from at least one of the following groups of elements: (a) lead (Pb), indium (In), thallium (Tl), cadmium (Cd) and bismuth (Bi); (b) copper (Cu) and magnesium (Mg); and (c) chromium (Cr) and manganese (Mn). The elements Pb, In, Tl, Cd and Bi can be used alone or in any combination and are employed in a total amount of from about 0.5-8 wt.%. Cu and Mg are employed alone or in a mixture thereof and are employed in an amount of from about 0.1-2 wt.%. Cr and Mn are employed alone or in a mixture thereof and are employed in an amount of from 0.1-1 wt.%.

The addition of 0.5-8 wt.% of Pb, In, Tl, Cd and/or Si to the bearing alloy improves the conformability and seizure resistance of the bearing material. An amount of less than 0.5 wt.% does not appreciably affect the properties of the alloys. Amounts greater than 8 wt.% are not desirable since they tend to decrease the melting point of the Sn. Additionally, the total addition quantity of these elements together with the addition quantity of the tin should not be more than about 35 wt.% since the fatigue resistance of the bearing alloy decreases as the combined amounts of these elements increases.

Cu and/or Mg can be contained in the bearing alloy of the invention in an amount of 0.1-2 wt.%. The Cu and/or Mg have an important effect on the hardness of the aluminum matrix and reduce the lowering of the hardness at high temperatures. The hardness of the alloy is increased as the amount of Cu and/or Mg is increased within this range whereas the seizure resistance decreases. Therefore, the amount of Cu and/or Mg employed is chosen so as to obtain a desired balance between the hardness and seizure resistance of the bearing alloy. An increase in the hardness of the alloy is not obtained with amounts of Cu and/or Mg of less than 0.1 wt.%. Amounts of these metals of more than 2.0 wt.% reduce the rolling property of the bearing alloy and lower the anti-corrosiveness. Furthermore, the Mg exists as a solid solution in the aluminum matrix and is liable to deposit during the annealing if the amount thereof is more than 2.0 wt.%.

The addition of 0.1-1 wt.% of Cr and/or Mn to a bearing alloy according to the present invention is also effective in preventing the lowering of the hardness of the alloy at high temperatures (although to a lesser extent than the addition of Cu and/or Mg) and in preventing the coarsening of Sn particles. When the quantity of the Cr and/or Mn is less than 0.1 wt.%, the improvement in high temperature hardness cannot be expected. The effect of the addition of amounts of more than 1.0 wt.% is not appreciable. The Cr and/or Mn form fine precipitates in the aluminum matrix. The Cr and/or Mn also serve to enhance the effects of the addition of the Cu and/or Mg and of the Pb, In, Tl, Cd and/or Bi.

The aluminum matrix of the bearing alloy according to the present invention preferably has a Vickers hardness (Hv) of from about 30 to 60. If the aluminum matrix is too soft, the load capacity of the bearing is insufficient and when a load is applied to the bearing, the silicon particles are pushed into the surface. If the aluminum matrix is too hard, when a shaft contacts the bearing surface, the silicon particles may be removed from the surface and will not become embedded again but will roll between the shaft and the bearing and cause excessive wear.

The aluminum base bearing alloy according to the present invention is prepared by melting aluminum in a gas furnace and adding desired amounts of Si and Sn and, depending on the desired properties of the alloy, the optional elements such as Pb, In, Cu, Cr and the like, to the molten aluminum according to the conventional techniques. The molten alloy is cast and the cast alloy is then subjected to steps of peeling; repeated (if necessary) rolling and annealing to obtain a sheet of the alloy of desired thickness; slitting; annealing; sanding; brushing and the like to obtain bearing alloy pieces. These pieces are then applied to backing steel sheets by conventional pressure welding techniques to obtain bimetal pieces which are then subjected to annealing and coiling. These annealed pieces can then be worked into plain bearings. The foregoing steps employed in the process of the present invention are, per se, known in the art relating to the preparation of aluminum base bearings and are disclosed, for example, in U.S. Pat. Nos. 3,078,563; 3,093,885; 3,104,135; 3,167,404; 3,300,836; 3,300,838 and 3,384,950. The processes for preparing aluminum base bearings disclosed in these patents are incorporated herein by reference.

Control of the size and number of nodular silicon particles in the bearing alloy which meet the limitations described above, i.e., at least 5 particles having a size of at least 5 μm, may be obtained by controlled annealing of the cast alloy according to conditions not previously disclosed in the art. Specifically, in the process employed in the present invention, during the rolling and annealing of the cast alloy, annealing is carried out at a temperature of 280°-550° C. for 1.5 to 6 hours. Following slitting, annealing is carried out at a temperature of greater than 350° C. and up to 550° C. for 1.5 to 6 hours followed by controlled cooling at a rate of less than 200° C. per hour. Following bonding to the backing steel by pressure welding, annealing is carried out at a temperature of 300°-400° C. for 1 to 2 hours.

The distinctions between the process employed in the present invention for obtaining the aluminum base bearing alloy and bearing composite wherein the alloy contains silicon particles of specified shape, size and number and the prior art processes may be better understood by referring to Table 1.

As noted previously, the aluminum base bearing composite according to the present invention is prepared by pressure welding the aluminum base bearing alloy according to the present invention to a backing steel according to conventional techniques and annealing the resultant composite at a temperature of 300° to 400° C. for 1 to 2 hours. The aluminum base bearing composite according to the present invention can be used as a bearing for internal combustion engines under conditions of high load without the need of a load overlayer, or overplate, which is required for conventional aluminum base bearings.

                                      TABLE 1                                      __________________________________________________________________________                                     Process Employed in                            Step         Prior Art Process(es)                                                                             Present Invention                              __________________________________________________________________________      (1)                                                                              Dissolution                                                                              Melting at 670-750° C.                                                                      ←                                         (2)                                                                              Casting   1.5-2.5 m/min       ←                                                     (1-2 m/min)                                                        (3)                                                                              Peeling   Reduce thickness about 2 mm                                                                        ←                                         (4)                                                                              Rolling   2-6 mm/pass         ←                                         (5)                                                                              Annealing 180-230° C. for about 1.5 hours                                                            280-550° C. for                                      (≦350° C. for about 1.5 hours)                                                      1.5 to 6 hours                                              Steps (4) and (5) repeated, if necessary                           (6)                                                                              Rolling   2-6 mm/pass         ←                                         (7)                                                                              Slitting  No conditions specified                                                                            ←                                         (8)                                                                              Annealing 180-230° C. for about 1.5 hours                                                            Greater than 350° C.-550°                                        C.                                                          No control of cooling speed                                                                       for 1.5 to 6 hours                                          (≦350° C. for about 1.5 hours                                                       Cooling speed: less than                                    No control of cooling speed)                                                                      200° C./hour                             (9)                                                                              Sanding   0.01-0.05 mm        ←                                        (10)                                                                              Brushing  No conditions specified                                                                            ←                                        (11)                                                                              Pre-heating                                                                              100-180° C.  ←                                                     (60-140° C.)                                               (12)                                                                              Sanding   0.005-0.05 mm       ←                                        (13)                                                                              Cleaning  Trichloroethylene   ←                                        (14)                                                                              Ni-plating                                                                               Thickness < 5 μm                                                                                ←                                        (15)                                                                              Pre-heating                                                                              80-230° C.   ←                                        (16)                                                                              Bonding   Reduction ratio: 45-55%                                                                            ←                                           (Pressure welding)                                                                       (45-60%)                                                          (17)                                                                              Annealing 180-230° C. for about 1.5 hours                                                            300-400° C. for 1-2 hours                            (≦350° C. for about 1.5 hours)                      (18)                                                                              Coiling   No conditions specified                                                                            ←                                        __________________________________________________________________________      Note:                                                                          (1) Conditions in parentheses are isolated teachings in the prior art.         (2) Steps (12)-(15) apply to the backing steel to which the alloy is           bonded in step (16).                                                     

The present invention may be better understood by referring to the accompanying drawings in light of the following description and data.

The seizure resistance, fatigue resistance and wear resistance data presented below and shown in the drawings were measured under conditions as described in Table 2. The seizure resistance test measures the static load necessary to cause seizure at constant oil temperature. The fatigue resistance test measures fatigue limits under dynamic load conditions and under forced lubrication with lubricant oil of a constant temperature and by using a quenched shaft material rotating at 3000 rpm and with 10⁷ times repetition of stressing. The wear resistance test measures the amount of wear of a bearing material at a constant load with respect to a shaft rotating at a constant speed over a definite period of time.

Aluminum base bearing alloys according to the present invention were prepared by a process as described above employing the conditions listed in Table 1. Each of the alloys contained, in addition to aluminum, 15 wt.%Sn, 3 wt.%Pb, 0.5 wt.%Cu, 0.4 wt.%Cr and an amount of Si as listed in Table A below. Each of the samples of Table A was annealed at a temperature of 350° C. for 1.5 hours in step (5) of the process (refer to Table 1). Cooling conditions following annealing were not controlled. Annealing and cooling conditions in step (8) of the process were controlled as listed in Table A so that each of the alloys contained per 3.56×10⁻² (mm)² of horizontal cross-sectional area, 31-35 nodular particles of Si having a size of 5-10 μm, 8-11 nodular particles of Si having a size of more than 10 and up to 17 μm, 4-6 nodular particles of Si having a size of more than 17 and up to 25 μm, and 1-3 nodular particles of Si having a size of more than 25 and up to 40 μm.

                  TABLE 2                                                          ______________________________________                                         Tester       Test Conditions                                                   ______________________________________                                         A - Seizure Tester                                                                          Shaft material: Nodular                                                        Lubricant type: SAE 5W-30                                                      Shaft surface roughness: 0.4-0.6 μm Ex                                      Oil temperature: 160 ± 2.5° C.                                       Rotation speed: 1000 rpm                                                       Shaft diameter: 52 mm                                                          Shaft hardness: Hv 200-300                                                     Urging load: 50 kg/cm.sup.2 /30 min                                            (increase gradually)                                                           Bearing surface roughness: 1-1.8 μm Rs                                      Bearing inner diameter: 52 mm                                     B - Fatigue Tester                                                                          Shaft material: AISI 1055 (forged)                                             Lubricant type: SAE 10W-30                                                     Shaft surface roughness: 0.8 μm Rz                                          Oil temperature: 140 ± 2.5° C.                                       Oil pressure: 5 kg/cm.sup.2                                                    Rotation speed: 3000 rpm                                                       Shaft diameter: 52 mm                                                          Shaft hardness: Hv 500-600                                                     Stress repetitions: 10.sup.7 times                                             Bearing surface roughness: 1-1.8 μm Rz                                      Bearing inner diameter and width:                                              52 × 20 mm                                                  C - Wear Tester                                                                             Shaft material: Nodular                                                        Lubricant type: Liquid paraffin                                                Shaft surface roughness: 0.8-0.9 μm Rz                                      Rotation speed: 100 rpm                                                        Shaft diameter: 40 mm                                                          Shaft hardness: Hv 200- 300                                                    Urging load: 50 kg                                                             Term of test: 5 hours                                             ______________________________________                                    

The seizure resistance of these alloys were measured employing the conditions for seizure tester A listed in Table 2. Each sample was tested three times under the same conditions. The range of seizure unit load values obtained are shown in FIG. 1.

For comparison, alloys of the same composition as those of Table A were prepared according to the same process but without control of the size and number of the Si particles by carrying out annealing in step (8) at 300° C. for 1.5 hours and by not controlling the cooling rate of the annealed samples. Seizure resistance of these alloys determined in the same manner as those of the alloys of Table A are shown in FIG. 2.

It may be seen by referring to the data of FIGS. 1 and 2 that the aluminum base bearing alloys of the present invention in which the shape, size and number of silicon particles are controlled, have uniformly better seizure resistance under conditions of high load and low viscosity oil than similar alloys prepared according to prior art procedures where there is no control of silicon particle formation.

                  TABLE A                                                          ______________________________________                                                     Annealing condition (Step (8)-Table 1)                                               Temperature        Cooling                                   Sample No.                                                                             Si (wt. %)                                                                               (°C.)                                                                              Time (Hr)                                                                              (°C./Hr)                           ______________________________________                                         1       1         475        4.5     120                                       2       3         450        4.0     140                                       3       5         425        3.5     160                                       4       7         400        3.0     180                                       5       9         375        2.5     190                                       6       11        360        2.0     200                                       7       13        360        1.5     200                                       8       15        360        1.5     200                                       ______________________________________                                    

The wear resistance of the alloys of Table A was measured according to the conditions listed for wear tester C in Table 2. The wear data for these alloys are shown in FIG. 3 (labelled "Control"). The wear resistance of alloys of the same composition but produced without control of the Si particles was similarly determined and the data are also shown in FIG. 3 (labelled "No control").

The aluminum base bearing alloys according to the present invention are seen to be markedly superior in wear resistance.

The fatigue resistance of the alloys of Table A was measured according to the conditions for fatigue tester B listed in Table 2. The fatigue unit load data is shown in FIG. 4. It is seen that the fatigue resistance of the alloys of the invention is gradually reduced as the Si content is increased within the range of 5-11 wt.%.

Aluminum base bearing alloys according to the present invention having the composition: Si 8 wt.%, Sn 15 wt.%, Pb 3 Wt.%, Cu 0.5 wt.%, Cr 0.4 wt.%, the balance being aluminum, were prepared according to the process described above and employing the conditions for the process employed in the present invention described in Table 1. Annealing conditions in step (8), Table 1, were varied to produce alloy samples A-1 to A-3, B-1 to B-3, C-1 to C-3, D-1 to D-3, and E-1 containing the distribution of nodular Si particles set forth in Table B.

                                      TABLE B                                      __________________________________________________________________________     Sample                                                                             No. of Si particles/3.56 × 10.sup.-2 (mm).sup.2                      No. less than 5 μm                                                                      5-10 μm                                                                          10 < -17 μm                                                                         17 < -25 μm                                                                         25 < -40 μm                                __________________________________________________________________________     A 1 185*     0   0       0       0                                               2 368*     0   0       0       0                                               3 623*     0   0       0       0                                             B 1 Bal      5   0       0       0                                               2 "       46   0       0       0                                               3 "       104  0       0       0                                             C 1 "       59   6       0       0                                               2 "       48   21      0       0                                               3 "       39   35      0       0                                             D 1 "       37   13      5       0                                               2 "       31   22      16      0                                               3 "       28   23      22      0                                             E 1 "       27   17      8       6                                             __________________________________________________________________________      *No. of particles having a size of 2.5-<5 μm.                         

The seizure resistance of alloy sample C-2 of Table B as compared to a conventional Al-Sn(20)-Cu(1) alloy as a function of oil temperature is shown in FIG. 5. The seizure resistance data was obtained according to the conditions of seizure tester A listed in Table 2 with the oil temperature varied as shown in FIG. 5. It is seen that the seizure resistance of each alloy decreases as the temperature of the lubricating oil increases but that the seizure resistance of the alloy of the invention is maintained at a relatively high level even at a high oil temperature.

FIG. 6 compares the seizure resistance of alloy sample No. C-2 of Table B with that of a conventional Al-Sn(20)-Cu(1) alloy for a forged shaft and for a nodular graphite cast iron shaft. The data of FIG. 6 was obtained employing the conditions of seizure tester A of Table 2 employing the different shafts. FIG. 6 illustrates that an aluminum base bearing alloy of the present invention provides markedly superior seizure resistance with the use of a nodular graphite cast iron shaft as compared to the conventional alloy.

To demonstrate the outstanding seizure, fatigue and wear resistance of the aluminum base bearing alloys according to the present invention having different Si contents, bearing alloys having an Sn content of 15 wt.%, Pb content of 3 wt.%, Cu content of 0.5 wt.%, Cr content of 0.4 wt.% and Si content as shown in Table C, the balance being Al, were prepared according to the process described above and employing the conditions of the process employed in the present invention listed in Table 1. The annealing conditions (step (8), Table 1) were varied to produce nodular Si particles having the number and size distribution listed in Table C. PG,23

                                      TABLE C                                      __________________________________________________________________________                                                                Wear                    Si                                  Seizure Unit Load                                                                       Fatigue Unit                                                                             (Tester             Sample                                                                             (Wt.                                                                              Silicon particles per 3.56 × 10.sup.-2 (mm).sup.2                                                         (Seizure tester                                                                         (Fatigue tester                                                                          C)                  No. %) <5 μm                                                                           5-10 μm                                                                          10 < -17 μm                                                                         17 < -25 μm                                                                         25 < -40 μm                                                                         (Kg/cm.sup.2)                                                                           (Kg/cm.sup.2)                                                                            (mm).sup.3          __________________________________________________________________________     A-1 5  Bal 0    0       0       0       450      800       5                   A-2 "  "   2    0       0       0       500      800       4                   A-3 "  "   5    0       0       0       700      800       3                   A-4 "  "   56   0       0       0       750      800       2.5                 A-5 "  "   48   23      0       0       800      800       2                   A-6 "  "   31   17      5       0       900      800       2                   A-7 "  "   26   15      6       2       950      750       2                   B-1 8  Bal 0    0       0       0       450      700       5                   B-2 "  "   3    0       0       0       550      700       4                   B-3 "  "   5    0       0       0       700      700       3.5                 B-4 "  "   61   0       0       0       800      650       3                   B-5 "  "   81   33      0       0       850      600       2.6                 B-6 "  "   53   25      6       0       900      600       2.5                 B-7 "  "   33   18      7       4       950      550       2.2                 C-1 11 Bal 0    0       0       0       500      600       7                   C-2 "  "   3    0       0       0       550      600       6                   C-3 "  "   5    0       0       0       600      600       5                   C-4 "  "   94   0       0       0       650      550       4                   C-5 "  "   71   38      0       0       700      500       3                   C-6 "  "   88   22      8       0       750      450       2.8                 C-7 "  "   26   18      11      8       800      400       2.5                 __________________________________________________________________________

The data of Table C demonstrates that for each of the Si contents, the seizure resistance and wear resistance of the alloy are increased as the number and size of the Si particles increase whereas the fatigue resistance is decreased slightly for bearing alloys containing larger Si particles.

Bearing alloys of the present invention having the compositions and nodular Si particle distribution shown in Table D (Sample Nos. 1-30) were prepared employing the process conditions listed in Table 1. For comparison, alloys containing only Si particles of less than 5 μm (Sample Nos. 31 and 32) and in which Si particle formation is not controlled (Sample Nos. 33 and 34) and conventional Al-Sn-Cu alloys (Sample Nos. 35 and 36) were also tested. The data of Table D show that aluminum base bearing alloys of the present invention containing, in addition to the Si and Sn, other elements including Pb, Cd, In, Tl, Bi, Cu, Mg, and Cr alone and in various combinations, also possess outstanding seizure resistance, fatigue resistance and wear resistance properties. The alloys of the invention have superior seizure, fatigue and wear resistance properties as compared to alloys not containing Si particles greater than 5 μm or in which Si particle formation is not controlled and to conventional Al-Sn-Cu alloys.

Although the present invention has been described in conjunction with certain preferred embodiments thereof, it is to be understood that the invention is not intended to be limited to these embodiments but, instead, is to include all those embodiments within the scope and spirit of the appended claims.

                                      TABLE D                                      __________________________________________________________________________     Si Particles/3.56 × 10.sup.-2 (mm).sup.2   Seizure                                                                             Fatigue                                                                             Wear                Sample                                                                             Wt.                                                                               Si particle size (μm)                                                                               Sn   Additional   (A)  (B)  (C)                 No. %  <5 5-10                                                                              10 < -17                                                                             17 < -25                                                                             25 < -40                                                                             (wt. %)                                                                             Elements (Wt. %)                                                                            Kg/cm.sup.2                                                                         Kg/cm.sup.2                                                                         (mm.sup.3)          __________________________________________________________________________      1  5  Bal                                                                                5 0     0     0     15   Cu(0.5)                                                                            Cr(0.4)  700  800  5                    2  "  "  25 11    4     1     10                850  550  2                    3  "  "  83 0     0     0     1.5  Pb(3)        750  600  4                    4  "  "  36 23    5     0     20   Cr(1)        850  750  2                    5  "  "  18 5     0     0     15   Cu(0.5)                                                                            Cr(0.4)  750  800  3                    6  "  "  31 28    11    4     10   Pb(5)                                                                              Cu(0.8)  900  550  2                    7  "  "  44 16    1     0     25   In(2)                                                                              Cu(1)    850  600  3                    8  "  "  103                                                                               0     0     0     5    Cu(0.1)                                                                            Cr(0.1)  750  750  4                    9  "  "  62 19    3     0     10   Tl(0.5)                                                                            Cr(0.8)  850  750  3                   10  "  "  48 15    0     0     35   Cu(2)        800  600  4                   11  8  "   5 0     0     0     15   Cu(0.5)                                                                            Cr(0.4)  700  700  5                   12  "  "  21 6     2     0     1.5  Cd(5)        850  550  4                   13  "  "  63 0     0     0     30   Pb(2)                                                                              In(1)                                                                              Cu(1)                                                                               750  550  6                   14  "  "  20 6     0     0     15   Pb(3)                                                                              Cu(0.5)                                                                            Mn(0.4)                                                                             800  600  5                   15  "  "  121                                                                               0     0     0     20   Mg(0.8)      800  500  6                   16  "  "  42 13    0     0     10   Mg(2)                                                                              Cr(1)    800  700  5                   17  "  "  36 19    8     2     5    Cr(0.3)      900  650  2                   18  "  "  29 21    11    0     10   Pb(1)                                                                              Cr(0.5)  900  650  2                   19  "  "  13 4     1     0     10   In(1)                                                                              Tl(1)                                                                              Cu(0.1)                                                                             800  550  3                   20  "  "  48 25    11    6     35   Cd(5)                                                                              Cu(0.5)                                                                            Mg(0.5)                                                                             800  500  3                   21  11 "   5 0     0     0     15   Pb(3)                                                                              Cu(0.5)                                                                            Cr(0.4)                                                                             650  600  7                   22  "  "  42 19    6     0     1.5               750  350  5                   23  "  "  26 15    4     1     10                800  350  5                   24  "  "  85 21    0     0     20   Cd(2)        700  350  6                   25  "  "  23 6     0     0     5    Bi(5)                                                                              Cu(1)    700  350  6                   26  "  "  41 33    21    0     15   Pb(5)                                                                              Cr(0.5)  800  450  4                   27  "  "  36 17    8     4     35   In(2)                                                                              Cu(2)                                                                              Mn(1)                                                                               800  450  2.5                 28  "  "  81 0     0     0     20   Cu(0.8)      700  350  7                   29  "  "  53 20    0     0     25   Cu(0.5)                                                                            Cr(0.4)  750  400  6                   30  "  "  32 5     0     0     10   In(0.5)                                                                            Tl(0.5)  650  350  6                    31*                                                                               5  "   0 0     0     0     --   Cu(1)        450  350  14                   32*                                                                               11 "   0 0     0     0     --   Cu(1)        500  350  11                   33*                                                                               1  x  x  x     x     x     --                300  400  22                   34*                                                                               3  x  x  x     x     x     --                400  400  16                   35*                                                                               0  -- -- --    --    --    20   Cu(1)        300  400  12                   36*                                                                               0  -- -- --    --    --    4    Cu(1)        250  400  18                  __________________________________________________________________________      *Comparison examples                                                           x No particle size control                                                

What is claimed is:
 1. An aluminum base bearing alloy consisting essentially of 5-11 wt.% Si, 1.5-35 wt.% Sn and, as the balance, aluminum, the alloy containing at least 5 particles of Si per 3.56×10⁻² (mm)² of cross-sectional area thereof, said particles being nodular and having a particle size of at least 5 μm.
 2. The aluminum base bearing alloy of claim 1, further comprising 0.5 to 8 wt.% of at least one element selected from the group consisting of Pb, In, Tl, Cd and Bi.
 3. The aluminum base bearing alloy of claim 1, further comprising 0.5-8 wt.% of at least one element selected from the group consisting of Pb, In, Tl, Cd and Bi, and 0.1-2 wt.% of at least one element selected from the group consisting of Cu and Mg.
 4. The aluminum base bearing alloy of claim 1, further comprising 0.5-8 wt.% of at least one element selected from the group consisting of Pb, In, Tl, Cd and Bi, 0.1-2 wt.% of at least one element selected from the group consisting of Cu and Mg and 0.1-1 wt.% of at least one element selected from the group consisting of Cr and Mn.
 5. The aluminum base bearing alloy of claim 1, further comprising 0.1-2 wt.% of at least one element selected from the group consisting of Cu and Mg.
 6. The aluminum base bearing alloy of claim 1, further comprising 0.1-2 wt.% of at least one element selected from the group consisting of Cu and Mg and 0.1-1 wt.% of at least one element selected from the group consisting of Cr and Mn.
 7. The aluminum base bearing alloy of claim 1, further comprising 0.1-1 wt.% of at least one element selected from the group consisting of Cr and Mn.
 8. The aluminum base bearing alloy of claim 1, further comprising 0.5-8 wt.% of at least one element selected from the group consisting of Pb, In, Tl, Cd and Bi, and 0.1-1 wt.% of at least one element selected from the group consisting of Cr and Mn.
 9. The aluminum base bearing alloy of claim 4, wherein the total amount of elements other than Al and Si, is less than 35 wt.%.
 10. A bearing material which is made by applying the aluminum base bearing alloy of any of claims 1-9, to a backing steel sheet by pressure welding. 